High density microfluidic devices are useful in a wide range of research, diagnostic and synthetic applications, including immunoassays, nucleic acid amplification and genomic analysis, cell separation and manipulation, and synthesis of radionuclides, organic molecules, and biomolecules. The advantages of microfluidic devices include conservation of reagents and samples, high density and throughput of sample analysis or synthesis, fluidic precision and accuracy, and a space reduction accompanying the replacement of counterpart equipment operating at the macrofluidic scale.
Efforts are being made to integrate microfluidic devices with existing high density and throughput testing equipment. Much of this conventional equipment relies on microtiter plates for holding, mixing, forming and reacting samples. The plates are typically flat glass or plastic trays in which an array of circular reagent wells are formed. Each well can typically hold between from a few microliters to hundreds of microliters of fluid reagents and samples, which may be loaded into the wells with automated delivery equipment. Plate readers are used to detect biological, chemical and/or physical events in the fluids placed in each well.
As the fields of combinatorial chemistry and high throughput screening have grown, so has equipment and laboratory instrumentation that has been designed to fill, manipulate and read microtiter plates. Unfortunately, independent equipment makers made little effort develop systems that were cross-compatible with the systems of other manufacturers. By the mid-1990s, the Society for Biomolecular Screening (SBS) formed a standards group to address these cross-compatibility problems. A final set of standards was published by SBS and the American National Standards Institute 2003.
These standards define the overall dimensions of a compliant microtiter plate, as well as the diameter, depth and spacing of the reagent wells in the plate. The plates may include 96, 384, 1536, etc., wells arranged in a 2:3 rectangular matrix. While some manufacturers have made plates packing even larger numbers of reagent wells into the dimensions of an SBS-formatted plate, the small-sizes of the wells can make filling and reading the plates more difficult.
The manipulation of fluid volumes on the order of nanoliters and picoliters has required many new discoveries and design innovations. There are fundamental differences between the physical properties of fluids moving in large channels and those traveling through micrometer-scale channels. See, e.g., Squires and Quake, 2005, Rev. Mod. Phys. 77, 977-1026; Stone et al., 2004, Annu. Rev. Fluid Mech. 36:381-411; and Beebe et al., 2002, Ann. Rev. Biomed. Eng. 4:261-86. For example, at a microfluidic scale the Reynolds number is extremely small, reflecting a difference in the ratio of inertial to viscous forces compared to fluids at macroscale. Fluids flowing in microfluidic systems exhibit reduced turbulence, electro-osmotic and laminar flow properties, and in other ways behave differently than observed at a macroscale.
Thus, there is a need for integrating microfluidic fluid delivery methods with conventional high efficiency and throughput testing equipment to effect efficient flow, containment and mixing of microfluids in this equipment. There is also a need to realize these microfluidic delivery methods in devices that can substitute for SBS formatted microtiter plates, so they can take advantage of the large amount of SBS-formatted equipment and instrumentation that is currently in use. These and other needs are addressed by the present invention.